In the field of fluid displacement, it is common practice to provide an impeller which is rotatable in a housing forming a flow passage or forming part of a flow passage and through which the impeller displaces the fluid generally axially, i.e. from an inlet side of an outlet side along the axis of rotation of the impeller. Depending upon the purpose of the fluid displacement device, it can be used to move volumes of the fluid from one place to another or to simply move around the fluid. The fluid itself can be a gas or gas mixture, in which case the fluid displacement apparatus can be a blower or fan. Alternatively the fluid can be a liquid, in which case the fluid displacement apparatus can be denominated a pump or an agitator or mixer.
Fluid-displacement apparatus of the aforedescribed type in the form of blowers are known and are generally driven with relatively low power electric motors. For electric power units of 10 kW or more, the electric motor is usually connected to the hub of the impeller or propeller by an efficiency-reducing transmission, the connections being made by flanging one part to another.
Blower units of this type are heavy, are bulky and generally require a special foundation. With an aligned arrangement of the hub of the transmission and the electric motor, the inflowing fluid flow lines are distorted and, in general, the flow characteristics through the unit can be adversely affected. In addition, this type of blower unit has an intolerable noise level when operated at high powers.